1. Field of the Invention
The present invention relates to a combustion-engined setting tool for driving fastening elements such as nails, bolts, and the like in a constructional component and that includes a combustion chamber which is being filled with an air-fuel mixture, and an inlet/outlet valve arrangement that connects the combustion chamber with tool openings which communicate with the environment.
2. Description of the Prior Art
In setting tools described above, fuel, such as, e.g., fuel gas, is combusted with an environmental air in the combustion chamber. Before each setting process, fresh air should be fed into the combustion chamber, and after each setting process, flue gases, which are produced during a combustion process, should be expelled from the combustion chamber.
In a conventional combustion-engined setting tool, such as Hilti GX 100 of the assignee herein, a setting piston is displaced in a piston guide that is adjoined, in the setting or drive-in direction, by a bolt guide. At the end of the piston guide remote from the bolt guide, there is provided a combustion chamber. The combustion chamber has a rear wall coaxially displaceable in the combustion chamber. When the setting tool is pressed against a constructional component, the rear wall is displaced away from the end of the combustion chamber adjacent to the piston guide up to the end of the combustion chamber remote from the piston guide, loading the return springs. The combustion chamber assumes an expanded position. Simultaneously with the expansion of the combustion chamber, fresh air is fed thereinto through the inlet/outlet valve. After completion of the setting process and lifting of the setting tool off the constructional component, the rear wall is displaced to its initial position by the biasing force of the return springs. As the combustion chamber collapses, the flue gases are expelled through the inlet/outlet valve. The advantage of the setting tool, which is described above, consists in that no accumulator or battery is needed, as the flushing of the combustion chamber is effected mechanically.
In this setting tool, the flue gas can be expelled from the setting tool in the same volume of the environment from which the fresh air is aspirated. This can result in contamination of the aspirated fresh air with the flue gas which can reduce the energy efficiency of the combustion process.
Accordingly, an object of the present invention is to provide a setting tool in which the drawback of the conventional setting tool is eliminated.